Process for upgrading light paraffins

ABSTRACT

The present invention relates to a process for producing aromatic compounds from a hydrocarbon gas containing C 3  through C 5  paraffinic hydrocarbons under conversion conditions in the presence of a catalyst comprising a borosilicate molecular sieve, a platinum metal component and a gallium metal component.

BACKGROUND OF THE INVENTION

The present invention is directed upgrading light paraffins such aspropane, and butanes. Interest in upgrading these light paraffins hasbeen growing due to recent and anticipated changes in refineryprocessing schemes which resulted and will result in a greater supply ofsuch light paraffins. These changes include: the higher severityoperation of the reforming process in order to maintain a high octanerating in the absence of or reduction of the lead content in gasoline;the lowering of reid vapor pressure (RVP) specifications; the increaseduse of oxygenates such as methyl tertiary butyl ether (MTBE) and ethanolresulting in the removal of butanes from the gasoline pool; theincreased demand for jet fuel necessitating increased gas oilhydrocracking resulting in more light gas production, and the increasein operating temperatures in fluidized catalytic crackers resulting inmore light gas production. Thus, there is great incentive to investigatemeans for converting these materials into more valuable liquids such astransportation fuels or chemical feedstocks.

The upgrading or conversion of light paraffinic gases and synthesis gashas previously been carried out in the presence of gallium-based orgallium-containing catalysts wherein such catalysts also contain varioustypes of molecular sieves.

U.S. Pat. No. 4,543,347 (Heyward et al.) discloses a catalystcomposition suitable for converting synthesis gas to hydrocarbons whichis a mixture of zinc oxide and an oxide of at least one metal selectedfrom gallium and iridium, an oxide of at least one additional metalcollected from the elements of Groups IB, II through V, VIB and VIIIincluding the lanthanides and actinides and a porous crystallinetectometallic silicate.

U.S. Pat. No. 4,490,569 (Chu et al.) discloses a process for convertingpropane to aromatics over a zinc-gallium zeolite This zeolite optionallymay also contain palladium. More specifically, the catalyst compositionused in the instant patent consists essentially of an aluminosilicatehaving gallium and zinc deposited thereon or an aluminosilicate in whichcations have been exchanged with gallium and zinc ions wherein thealuminosilicate is selected from the group known as ZSM-5 type zeolites.

U.S. Pat. No. 4,585,641 (Barri et al.) discloses crystallinegallosilicates which may be impregnated, ion-exchanged, admixed,supported or bound for catalyzing a reaction such as alkylation,dealkylation, dehydrocyclodimerization, transalkylation, isomerization,dehydrogenation, hydrogenation, cracking, hydrocracking, cyclization,polymerization, conversion of carbon monoxide and hydrogen mixturesthrough hydrocarbons and dehydration reaction. The metal compounds whichmay be used for ion exchange or impregnation may be compounds of any oneof the groups of metals belonging to Groups IB, IIB, IIIA, IVA, VA, VIB,VIIB and VIII according to the Periodic Table. Specifically, preferredcompounds include copper, silver, zinc, aluminum, gallium, indium,vanadium, lead, antimony, bismuth, chromium, molybdenum, tungsten,manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium,platinum, radium, thorium and the rare earth metals. Patentees describetheir gallosilicate as "Gallo Theta-1" in contradistinction to anMFI-type gallosilicate which has a substantially different X-raydiffraction pattern.

U.S. Pat. No. 4,350,835 (Chester et al.) relates to a catalytic processfor converting gaseous feedstocks containing ethane to liquid aromaticsby contacting the feed in the absence of air or oxygen under conversionconditions with a crystalline zeolite catalyst having incorporatedtherein a minor amount of gallium thereby converting the ethane toaromatics. The gallium is present in the catalyst as gallium oxide or asgallium ions if cations in the aluminosilicate have been exchanged withgallium ions. The patent further discloses that the original alkalimetal of the zeolite, when it has been synthesized in the alkali metalform, may be converted to the hydrogen form or be replaced by ionexchange with other suitable metal cations of Groups I through VIII ofthe Periodic Table, including nickel, copper, zinc, palladium, calciumor rare earth metals.

European Patent Specification 0 050 021 discloses a process forproducing aromatic hydrocarbons from a hydrocarbon feedstock containingat least 70 wt. % C₂ with a catalyst composition comprising analuminosilicate having gallium deposited thereon and/or analuminosilicate in which cations have been exchanged with gallium ions,where the aluminosilicate has a silica to alumina molar ratio of atleast 5:1.

European patent application 0 107 876 discloses a process for producingan aromatic hydrocarbon mixture from a feedstock containing more than 50wt. % C₂ through C₄ paraffins. Specifically, the process is carried outin the presence of crystalline gallium-silicate having a SiO₂ /Ga₂ O₃molar ratio of 25 to 250 and a Y₂ O₃ /GaO₃ molar ratio lower than 1where Y can be aluminum, iron, cobalt or chromium. The disclosure alsoteaches a two-step silicate treatment comprising a coke deposition and acoke burn-off with an oxygen-containing gas.

European patent application 0 107 875 similarly discloses a process forproducing an aromatic hydrocarbon mixture from a feedstock comprisingmore than 50 wt. % of C₂ through C₄ paraffins This process is carriedout in the presence of a crystalline gallium-silicate, having a SiO₂/Ga₂ O₃ molar ratio of 25 to 100 and a Y₂ O₂ /Ga₂ O₃ molar ratio lowerthan 1 where Y can be aluminum, iron, cobalt or chromium.

Other patents that disclose processes for upgrading light paraffinsusing gallium-containing catalysts include:

U.S. Pat. No. 4,613,716 McNiff)

U.S. Pat. No. 4,766,264 (Bennett et al.)

U.S. Pat. No. 4,276,437 (Chu)

U.S. Pat. No. 4,629,818 (Burress)

Light paraffinic gases have also been upgraded to liquid aromatics inthe presence of crystalline aluminosilicate zeolite catalysts havingincorporated therein a minor amount of a metal selected from GroupsVIII, IIB, and IB of the Periodic Table. For instance, U.S. Pat. No.4,120,910 (Chu) discloses copper-zinc-HZSM-5, platinum-HZSM-5,copper-HZSM-5, and zinc-HZSM-5 catalysts suitable for upgrading agaseous paraffinic hydrocarbon feed to aromatic compounds.

U.S. Pat. No. 4,704,494 (Inui) discloses a process for the conversion oflow molecular paraffin hydrocarbons to aromatic hydrocarbons in thepresence of metallosilicates wherein the metal is Al, Ga, Ti, Zr, Ge,La, Mn, Cr, Sc, V, Fe, W, Mo, or Ni.

International Application No. PCT/GB84/00109 (International PublicationNumber: WO84/03879) (Barlow) discloses an aromatization processutilizing a catalyst having a Group VIII metal in combination with agalloaluminosilicate.

It has now been discovered that C₃ through C₅ light paraffins can mosteffectively be upgraded by the catalytic process of the presentinvention minimizing methane and ethane production while simultaneouslymaximizing the production of benzene, toluene, and xylenes.

The process of the present invention involves the use of an AMS-lBcrystalline borosilicate molecular sieve. This sieve is disclosed inU.S. Pat. Nos. 4,268,420 and 4,269,813 (both to Klotz) both of which areincorporated herein by reference. The '420 patent broadly discloses theuse of the AMS-lB crystalline borosilicates for various hydrocarbonconversion processes and chemical adsorption. Some of the hydrocarbonconversion processes for which the borosilicates appear to haverelatively useful catalytic properties are fluidized catalytic cracking;hydrocracking; the isomerization of normal paraffins and naphthenes; thereforming of naphthas and gasoline-boiling-range feedstocks; theisomerization of aromatics, especially the isomerization ofalkylaromatics, such as xylenes; the disproportionation of aromatics,such as toluene, to form mixtures of other more valuable productsincluding benzene, xylene, and other higher methyl-substituted benzenes;hydrotreating; alkylation; hydrodealkylation; hydrodesulfurization; andhydrodenitrogenation. They are particularly suitable for theisomerization of alkylaromatics, such as xylenes, and for the conversionof ethylbenzene. The AMS-lB borosilicates, in certain ion-exchangedforms, can be used to convert alcohols, such as methanol, to usefulproducts, such as aromatics or olefins.

It should also be noted that hydrogen processing catalysts containing anAMS-lB borosilicate molecular sieve coupled with catalytic metalcomponents are also known. For instance, U.S. Pat. No. 4,434,047(Hensley, Jr. et al.) discloses a catalytic dewaxing hydrotreatingprocess using a catalyst containing a shape-selective cracking componentsuch as an AMS-lB borosilicate molecular sieve, and a hydrogenatingcomponent containing Cr, at least one other Group VIB metal and at leastone Group VIII metal. U.S. Pat. No. 4,268,420 similarly discloses anAMS-lB crystalline borosilicate which can be used in intimatecombination with a hydrogenating component, such as tungsten, vanadium,molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noblemetal, such as platinum or palladium, or rare earth metals, where ahydrogenation-dehydrogenation function is to be performed.

U.S. Pat. No. 4,563,266 (Hopkins et al.) discloses an AMS-lB crystallineborosilicate molecular sieve combined with at least one Group VIII noblemetal for use in a catalytic dewaxing process. U.S. Pat. No. 4,738,768(Tait et al.) likewise discloses the use of an AMS-lB borosilicate in ahydrocarbon pour point reducing process.

U.S. Pat. No. 4,451,685 (Nevitt et al.) discloses a process to convertpropylene to gasoline blending stock products. Specifically, C₂ throughC₃ olefins are converted to a mixture of C₄ through C₈ aliphatics and C₆through C₉ aromatics in the presence of hydrogen and a catalyst. Thecatalyst employed is a crystalline AMS-lB borosilicate that may beimpregnated with catalytically active materials including the metals ofGroups IB, IIA, IIIA, IIIB, IVB, VB, VIB, VIIB and VIII and rare earthelements.

U.S. Pat. No. 4,433,190 (Sikkenga et al.) discloses a process to convertsubstantially linear alkanes such as normal alkanes having two to twentycarbon atoms to dehydrogenated and isomerized products in the presenceof hydrogen and an AMS-lB crystalline borosilicate-based catalystcomposition. This catalyst contains a noble metal and may also containan ion or molecule of a Group IB, IIIB, IVB, VB, VIB, VIIB or VIII metalor a rare earth element.

Finally, U.S. Pat. No. 4,766,265 (Desmond) teaches a process for theconversion of ethane to liquid aromatic compounds using a catalystcontaining a gallium impregnated molecular sieve with both a rheniumcomponent and a metal selected from the group consisting of nickel,palladium, platinum, rhodium and iridium. The molecular sieve can be analumino-, gallo-, or borosilicate. The '265 process is directed tohandling ethane rich feedstocks ranging from 100% ethane to a feedstockcontaining only minor amounts of ethane in a feedstock predominantly ofhydrogen, methane and relatively minor amounts of C₂ -C₅ olefins and C₃-C₅ paraffins.

In contrast to the '265 process, the process of the present invention isdirected to the conversion of a hydrocarbon gas rich in C₃ through C₅light paraffins, preferably a feedstock rich in either C₃ and/or C₄Further, the process of the present invention does not require thepresence of a rhenium metal component in the catalyst.

It has now been discovered that C₃ through C₅ paraffins can mosteffectively be upgraded by the catalytic process of the presentinvention minimizing methane and ethane production while simultaneouslymaximizing the production of benzene, toluene and xylenes.

SUMMARY OF THE INVENTION

Briefly stated, in a broad aspect, this invention relates to a processfor producing aromatic compounds from a hydrocarbon gas rich inparaffinic hydrocarbons ranging from C₃ to C₅ under conversionconditions in the presence of a catalyst comprising a borosilicatemolecular sieve, a platinum metal component and a gallium metalcomponent.

DETAILED DESCRIPTION OF THE INVENTION

The present invention deals with the conversion of a hydrocarbon gasrich in paraffinic hydrocarbons ranging from C₃ to C₅ to aromatics. Aparticularly suitable feedstock for use in the present inventioncontains C₃ and/or through C₄ light paraffins. The feedstock suitablefor use in the present invention preferably contains less than 10%ethane and most preferably a relatively minor amount of ethane such asless than 5%. Minor amounts of methane can also be present. In additionto the mentioned paraffins, the feedstock may contain other light gasessuch as propylene, butene, isobutene, butadiene, and paraffins andolefins with five or more carbon atoms per molecule. These feedstocksare generally available from several sources in a refinery as elucidatedabove.

The process of the invention provides for the direct conversion of thelight paraffinic gases to valuable aromatic hydrocarbons such asbenzene, toluene, and xylenes. These aromatics can be used as anadditive component to increase the octane number of gasoline or as rawmaterials in the petrochemical industry.

The process of the invention selectively provides for a high yield ofbenzene, toluene, and xylenes in the C₄ + product fraction whileminimizing the yield of light C₁ and C₂ gases and C₉ + aromaticcompounds in the product fraction.

Broadly, the catalyst employed according to the process of the presentinvention comprises a borosilicate molecular sieve component, a platinummetal component and a gallium metal component.

The catalyst system which is useful in this invention comprises aborosilicate catalyst system based on a molecular sieve materialidentified as AMS-lB. Details as to the preparation of AMS-lB aredescribed in U.S. Pat. No. 4,269,813. Such AMS-lB crystallineborosilicate generally can be characterized by the X-ray pattern listedin Table I and by the composition formula:

    0.9±0.2 M.sub.2/n O : B.sub.2 O.sub.3 : ySiO.sub.2 : zH.sub.2 O

wherein M is at least one cation, n is the valence of the cation, y isbetween 4 and about 600 and z is between 0 and about 160.

                  TABLE I                                                         ______________________________________                                        d-Spacing Å (1)                                                                         Assigned Strength (2)                                           ______________________________________                                        11.2 ± 0.2  W-VS                                                           10.0 ± 0.2 .sup.  W-MS                                                     5.97 ± 0.07                                                                              W-M                                                             3.82 ± 0.05                                                                              VS                                                              3.70 ± 0.05                                                                              MS                                                              3.62 ± 0.05                                                                                M-MS                                                          2.97 ± 0.02                                                                              W-M                                                             1.99 ± 0.02                                                                              VW-M .sup.                                                      ______________________________________                                         (1) Copper K alpha radiation                                                  (2) VW = very weak; W = weak; M = medium; MS = medium strong; VS = very       strong                                                                   

The AMS-lB borosilicate molecular sieve useful in this invention can beprepared by crystallizing an aqueous mixture, at a controlled pH, ofsources for cations, an oxide of boron, an oxide of silicon, and anorganic template compound.

Typically, the mole ratios of the various reactants can be varied toproduce the crystalline borosilicates of this invention. Specifically,the mole ratios of the initial reactant concentrations are indicatedbelow:

    ______________________________________                                                                      Most                                                        Broad     Preferred                                                                             Preferred                                       ______________________________________                                        SiO.sub.2 /B.sub.2 O.sub.3                                                                  5-400       10-150   10-80                                      R.sub.2 O.sup.+ /[R.sub.2 O.sup.+ + M.sub.2/n O]                                            0.1-1.0     0.2-0.97 0.3-0.97                                   OH.sup.- /SiO.sub.2                                                                         0.01-11     0.1-2    0.1-1                                      H.sub.2 O--OH.sup.-                                                                         10-4000     10-500   10-500                                     ______________________________________                                    

wherein R is an organic compound and M is at least one cation having avalence n, such as an alkali metal or an alkaline earth metal cation. Byregulation of the quantity of boron (represented as B₂ O₃) in thereaction mixture, it is possible to vary the SiO₂ /B₂ O₃ molar ratio inthe final product.

More specifically, the material useful in the present invention isprepared by mixing a cation source compound, a boron oxide source, andan organic template compound in water (preferably distilled ordeionized). The order of addition usually is not critical although atypical procedure is to dissolve sodium hydroxide and boric acid inwater and then add the template compound. Generally, after adjusting thepH, the silicon oxide compound is added with intensive mixing such asthat performed in a Waring Blender. After the pH is checked andadjusted, if necessary, the resulting slurry is transferred to a closedcrystallization vessel for a suitable time. After crystallization, theresulting crystalline product can be filtered, washed with water, dried,and calcined.

During preparation, acidic conditions should be avoided. When alkalimetal hydroxides are used, the values of the ratio of OH^(-/SiO) ₂ shownabove should furnish a pH of the system that broadly falls within therange of about 9 to about 13.5. Advantageously, the pH of the reactionsystem falls within the range of about 10.5 to about 11.5 and mostpreferably between about 10.8 and about 11.2.

Examples of oxides of silicon useful in this invention include silicicacid, sodium silicate, tetraalkyl silicates and Ludox, a stabilizedpolymer of silicic acid manufactured by E. I. du Pont de Nemours & Co.Typically, the oxide of boron source is boric acid although equivalentspecies can be used such as sodium borate and other boron-containingcompounds.

Cations useful in formation of AMS-lB include alkali metal and alkalineearth metal cations such as sodium, potassium, lithium, calcium andmagnesium. Ammonium cations may be used alone or in conjunction withsuch metal cations. Since basic conditions are required forcrystallization of the molecular sieve of this invention, the source ofsuch cation usually is a hydroxide such as sodium hydroxide.Alternatively, AMS-lB can be prepared directly in the hydrogen form byreplacing such metal cation hydroxides with an organic base such asethylenediamine.

Organic templates useful in preparing AMS-lB crystalline borosilicateinclude alkylammonium cations or precursors thereof such astetraalkylammonium compounds. A useful organic template istetra-n-propyl-ammonium bromide. Diamines, such as hexamethylenediamine,can be used.

In a more detailed description of a typical preparation of thisinvention, suitable quantities of sodium hydroxide and boric acid (H₃BO₃) are dissolved in distilled or deionized water followed by additionof the organic template. The pH may be adjusted between about 11.0±0.2using a compatible acid or base such as sodium bisulfate or sodiumhydroxide. After sufficient quantities of silicic acid polymer (Ludox)are added with intensive mixing, preferably the pH is again checked andadjusted to a range of about 11.0±0.2. The resulting slurry istransferred to a closed crystallization vessel and reacted usually at apressure at least the vapor pressure of water for a time sufficient topermit crystallization which usually is about 0.25 to about 20 days,typically is about one to about ten days and preferably is about five toabout seven days, at a temperature ranging from about 100° to about 250°C., preferably about 125° to about 200° C. The crystallizing materialcan be stirred or agitated as in a rocker bomb. Preferably, thecrystallization temperature is maintained below the decompositiontemperature of the organic template compound. Especially preferredconditions are crystallizing at about 165° C. for about five to aboutseven days. Samples of material can be removed during crystallization tocheck the degree of crystallization and determine the optimumcrystallization time.

The crystallization material formed can be separated and recovered bywell-known means such as filtration with washing. This material can bemildly dried for anywhere from a few hours to a few days at varyingtemperatures, typically about 25°-200° C., to form a dry cake which canthen be crushed to a powder or to small particles and extruded,pelletized, or made into forms suitable for its intended use. Typically,materials prepared after mild drying contain the organic templatecompound and water of hydration within the solid mass and a subsequentactivation or calcination procedure is necessary, if it is desired toremove this material from the final product. Typically, mildly driedproduct is calcined at temperatures ranging from about 260° to about850° C. and preferably about 525° to about 600° C. Extreme calcinationtemperatures or prolonged crystallization times may prove detrimental tothe crystal structure or may totally destroy it. Generally there is noneed to raise the calcination temperature beyond about 600° C. in orderto remove organic material from the originally formed crystallinematerial. Typically, the molecular sieve material is dried in a forceddraft oven at 165° C. for about 16 hours and is then calcined in air ina manner such that the temperature rise does not exceed 125° C. per houruntil a temperature of about 540° C. is reached. Calcination at thistemperature usually is continued for about 4 to 16 hours.

Although not required, it is preferred to employ the above-describedborosilicate molecular sieve combined, dispersed or otherwise intimatelyadmixed in a matrix of at least one non-molecular sieve, porousrefractory inorganic oxide matrix component, as the use of such a matrixcomponent facilitates the provision of the ultimate catalyst in a shapeor form well suited for process use. Useful matrix components includealumina, silica, silica-alumina, zirconia, titania, etc., and variouscombinations thereof. The matrix components also can contain variousadjuvants such as phosphorus oxides, boron oxides, and/or halogens suchas fluorine or chlorine. Usefully, the molecular sieve-matrix dispersioncontains about 1 to 99 wt. % of a sieve component, preferably 20 toabout 90 wt. % and most preferably 30 to 80 wt. % of a sieve componentbased upon the sieve-matrix dispersion weight.

Methods for dispersing molecular sieve materials within a matrixcomponent are well-known to persons skilled in the art and applicablewith respect to the borosilicate molecular sieve materials employedaccording to the present invention. A method is to blend the molecularsieve component, preferably in finely-divided form, in a sol, hydrosolor hydrogel of an inorganic oxide, and then add a gelling medium such asammonium hydroxide to the blend, with stirring, to produce a gel. Theresulting gel can be dried, shaped if desired, and calcined. Dryingpreferably is conducted in air at a temperature of about 80° to about350° F. (about 27° to about 177° C.) for a period of several seconds toseveral hours. Calcination preferably is conducted by heating in air atabout 800° to about 1,200° F. (about 427° to about 649° C.) for a periodof time ranging from about 1/2 to about 16 hours.

Another suitable method for preparing a dispersion of the molecularsieve component in a porous refractory oxide matrix component is to dryblend particles of each, preferably in finely-divided form, and thenshape the dispersion if desired.

Alternatively, in another method, the sieve and a suitable matrixmaterial like alpha-alumina monohydrate such as Conoco Catapal SBAlumina can be slurried with a small amount of a dilute weak acid suchas acetic acid, dried at a suitable temperature under about 200° C.,preferably about 100° to about 150° C. and then calcined at betweenabout 350° and about 700° C., more preferably between about 400° toabout 650° C.

Silica-supported catalyst compositions can be made by dry mixing theborosilicate sieve with a silica source such as Cab-O-Sil, adding waterand stirring. The resulting solid is then dried below about 200° C. andfinally calcined between about 350° C. and 700° C.

A catalytically active metal component present in the catalyst of theinstant invention can be placed onto the borosilicate structure by ionexchange, impregnation, a combination thereof, or other suitable contactmeans. Before placing a catalytically active metal ion or compound onthe borosilicate structure, the borosilicate may be in the hydrogen formwhich, typically, is produced by exchange one or more times withammonium ion, typically using ammonium acetate, followed by drying andcalcination as described above.

The metal components of the catalyst employed according to the presentinvention can be present in elemental form, as oxides, as nitrates, aschlorides or other inorganic salts, or as combinations thereof. Whileother Group VIII metals can be employed in the present invention,platinum is preferred because it is relatively inactive forhydrogenolysis which would result in undesirable increased yields of C₁and C₂. Relative proportions of the sieve component, the platinum metalcomponent and the gallium metal component are such that at least acatalytically-effective amount of each is present.

The platinum metal component content preferably ranges from about 0.01to about 10 wt. %, calculated as a zero valent metal and being based onthe total weight of the catalytic final composite, with about 0.01 toabout 5 wt. % being more preferred, with a range of 0.05 to 1.0 wt. %being most preferred. Higher levels of platinum can be employed ifdesired, though the degree of improvement resulting therefrom typicallyis insufficient to justify the added cost of the metal.

The gallium metal component content preferably ranges from about 0.01 toabout 10 wt. % calculated as the zero valent metal and based on thetotal weight of the final catalytic composite, a range of from 0.1 to 8wt. % being more preferred and with a range of 0.5 to 5 wt. % being mostpreferred.

The platinum and gallium metal components of the catalyst employedaccording to this invention can be associated with the sieve componentby impregnation of the sieve component, or the sieve component can bedispersed in a porous refractory inorganic oxide matrix, with one ormore solutions of compounds of the platinum metal component and galliummetal component which compounds are convertible to oxides oncalcination. It also is contemplated, however, to impregnate a porousrefractory inorganic oxide matrix component with such solutions of theplatinum metal component and gallium metal component and then blend thesieve component with the resulting impregnation product. Accordingly,the present invention contemplates the use of catalysts in which theplatinum metal and gallium metal components are deposed on the sievecomponent, on a sieve-matrix component dispersion or on the matrixcomponent of a sieve-matrix component.

The mechanics of impregnating the sieve component, matrix component orsieve-matrix component with solutions of compounds convertible to metaloxides on calcination are well-known to persons skilled in the art andgenerally involve forming solutions of appropriate compounds in suitablesolvents, preferably water, and then contacting the sieve matrixcomponent or sieve matrix dispersion with an amount or amounts ofsolution or solutions sufficient to deposit appropriate amounts of metalor metal salts onto the sieve or sieve matrix dispersion. Useful metalcompounds convertible to oxides are well-known to persons skilled in theart and include various ammonium salts as well as metal acetates,nitrates, anhydrides, etc.

In another embodiment of the present invention the catalyst of thepresent invention also contains chloride. The addition of chloride tothe catalyst serves to increase the conversion and selectivity of theprocess of the invention to aromatics. A convenient method of adding thechloride is to include a predetermined volume of a solution containing apredetermined concentration of hydrochloric acid in the impregnatingsolution used to incorporate the platinum metal component with thecatalyst.

Alternatively, the chloride can also be added during the impregnation ofthe metal salt if the metal salt contains chloride, such as hydrogenhexachloroplatinate (H₂ PtCl₆.6H₂ O) If the chloride content in thechloride-containing metal salt is not sufficiently high, additionalchloride can be added by the addition of hydrochloric acid to theimpregnating solution.

In the instant embodiment of the invention, the catalyst broadlycontains 0.1 to 10 wt. % chloride, preferably 0.5 to 5 wt. % chlorideand most preferably 0.5 to 1.5 wt. % chloride based on the finalcatalyst weight.

Also contemplated within the purview of the present invention, chloridecan be incorporated into the catalyst by the addition ofchloride-containing compounds to the feed stream such as carbontetrachloride, hydrochloric acid, in amounts such that the finalcatalyst contains the above prescribed amount of chloride.

The above-described catalysts can be employed in any suitable form suchas spheres, extrudates, pellets, or C-shaped or cloverleaf-shapedparticles.

The process of the present invention is carried out under suitableoperating conditions set out below in Table II under which the feed iscontacted with the above-described catalyst. It is also contemplatedthat a portion of the unconverted effluent stream can be recycled to thefeed after separation from the aromatic products.

                  TABLE II                                                        ______________________________________                                                                          Most                                        Conditions    Broad      Preferred                                                                              Preferred                                   ______________________________________                                         Temperature, °F.                                                                    700-1400   800-1200 850 -1150                                   Total Pressure, psig                                                                         0-500      0-300    0-100                                      WHSV, h.sup.-1                                                                              0.1-100    0.1-40   0.1-20                                      ______________________________________                                    

The present invention is described in further detail in connection withthe following examples, it being understood that the same are forpurposes of illustration only and not limitation.

EXAMPLE 1

The present example demonstrates the process of the invention as itcontrasts with two comparative processes.

The catalyst used in accordance with the present invention was preparedwith a base composed of 40 wt. % AMS-lB borosilicate molecular sievedispersed in 60 wt. % PHF gamma-alumina. This base was hot-exchangedwith an aqueous ammonium acetate solution at 90°-100° C., then dried atabout 250° F. followed by calcination at 900°-1000° F. This base wasimpregnated with an aqueous solution of gallium nitrate hydrate toresult in a final catalyst having 1.0 wt. % Ga. The Ga-impregnated basewas then dried at about 250° F. and calcined at 900°-1000° F. ThisGa-containing base was then impregnated with an aqueous solution oftetraamineplatinum (II) nitrate to yield a final catalyst having 0.1 wt.% Pt. The Pt-impregnated-Ga-containing base was then dried at about 250°F. and then calcined at 900°-1000° F.

Two comparative catalysts, catalyst A and catalyst B were prepared in asimilar manner as the catalyst of the invention except catalyst A didnot contain any metals whereas catalyst B contained only gallium and noplatinum. The gallium was present in catalyst B in the same amount as inthe above-exemplified catalyst of the invention. The process of theinvention and the comparative processes utilizing catalysts A and B weretested for propane conversion in a continuous-flow fixed-bed reactorunder the following conditions:

Temperature=994° F.

Total pressure=50 psig

Catalyst weight=1.5 g

Propane liquid rate=24 ml/h

Nitrogen diluent rate=100 cc(NTP)/min

In each case the catalyst was pretreated in situ with nitrogen at about1000° F. for 0.5 hours followed by a hydrogen treatment at about 1000°F. for 1 hour. The results are set out below in Table III where productselectivities and total conversion are shown in wt. %.

                  TABLE III                                                       ______________________________________                                                 Invention                                                                             Comparative A                                                                             Comparative B                                    ______________________________________                                        Methane    6.1       26.9        13.8                                         Ethane +   29.4      68.6        41.1                                         Ethylene                                                                      C4+ aliphatics                                                                           22.9      4.5         15.7                                         Benzene    6.8       0           6.3                                          Toluene    18.2      0           15.1                                         Xylenes    13.4      0           8.0                                          C9+ aromatics                                                                            3.2       0           0                                            Total conversion                                                                         8.2       3.6         5.5                                          Hours on stream                                                                          5         3           2                                            ______________________________________                                    

The process of the invention clearly manifested the least methane, andethane plus ethylene selectivity coupled with the highest selectivityfor benzene, toluene, and xylenes.

What is claimed is:
 1. A process for converting a gaseous hydrocarbonfeed containing C₃ through C₅ paraffinic hydrocarbons to aromatichydrocarbons which comprises contacting the feed under conversionconditions with a catalyst composition comprising a borosilicatemolecular sieve, a platinum metal component and a gallium metalcomponent.
 2. The process of claim 1 wherein the gaseous feed comprisesC₃ and C₄ paraffins.
 3. The process of claim 2 wherein the gaseous feedcomprises butane.
 4. The process of claim 1 wherein the borosilicatemolecular sieve is dispersed within a non-molecular sieve containingporous refractory inorganic oxide matrix component.
 5. The process ofclaim 1 wherein the platinum metal component is present in an amountranging from about 0.01 to about 10 wt. % calculated as the zero valentmetal and based on the total weight of the composition.
 6. The processof claim 1 wherein the gallium metal component is present in an amountranging from about 0.01 to about 10 wt. % calculated as the zero valentmetal and based on the total weight of the composition.
 7. The processof claim 4 wherein the borosilicate molecular sieve is present in thedispersion such that the weight of the borosilicate ranges from about 20to about 90 wt. % based on the weight of the borosilicate-refractoryinorganic oxide dispersion.
 8. The process of claim 4 wherein theborosilicate molecular sieve is present in the dispersion such that theweight of the borosilicate ranges from about 30 to 80 wt. % based on theweight of the borosilicate-refractory inorganic oxide dispersion.
 9. Theprocess of claim 4 wherein the refractory inorganic oxide component isselected from a group consisting of silica, silica-alumina, and alumina.10. The process of claim 1 wherein the platinum metal component ispresent in an amount ranging from about 0.01 to about 5 wt. % calculatedas the zero valent metal and based on the total weight of thecomposition.
 11. The process of claim 1 wherein the gallium metalcomponent is present in an amount ranging from about 0.1 to about 8 wt.% calculated as the zero valent metal and based on the total weight ofthe composition.
 12. The process of claim 1 wherein the platinum metalcomponent is present in an amount ranging from about 0.05 to about 1.0wt. % and the gallium metal component is present in an amount rangingfrom about 0.5 to about 5 wt. % both calculated as the zero valent metaland based on the total weight of the final composition.
 13. The processof claim 7 wherein the platinum metal component is present in an amountranging from about 0.05 to about 1.0 wt. % and the gallium metalcomponent is present in an amount ranging from about 0.5 to about 5 wt.% both calculated as the zero valent metal and based on the total weightof the final composition.
 14. The process of claim 8 wherein theplatinum metal component is present in an amount ranging from about 0.05to about 1.0 wt. % and the gallium metal component is present in anamount ranging from about 0.5 to about 5 wt. % both calculated as thezero valent metal and based on the total weight of the finalcomposition.